The record of atmospheric CO2 derived from the stable carbon isotopic composition of buried plant in perennial frozen lacustrine sediments

The δ13C values of well-preserved submersed plant tissues of Potamogeton pectinatus in a 200-cm perennial frozen lacustrine sediment of Ngoring Lake, representing the age from 9.17 to 2.17 ka BP, range from −17.67‰ to −11.39‰, and have a decreasing trend from bottom to top with obvious shifts at 6.77 and 4.56 ka BP. According to the model of carbon isotopic fractionation in submersed plant, an approach that can be used to estimate the atmospheric CO2 change is developed because the δ13C of submersed plant is the function of the dissolved CO2 concentration. The calculated results show that the atmospheric CO2 concentration had an increasing tendency from 9.16 to 2.17 ka BP, and can be divided into three periods similar to the carbon isotope composition. The obvious shifts of δ13C in submersed plant tissues represent twice leaps of atmospheric CO2 at 6.77 and 4.56 ka BP with average increase of approximately 30 and 45 ppmv in concentration, respectively.